Section 101. The commissioner of food and agriculture shall establish and promulgate official grades of apples packed or repacked within the commonwealth, and may from time to time amend or modify such grades. Before establishing, amending or modifying any such grades, the commissioner shall consult with growers and shippers of apples relative to proposed grades, or, upon written petition of twenty-five or more growers producing annually an aggregate of not less than one hundred thousand bushels of apples, the commissioner shall, after reasonable notice, specifying the date, place and purpose of the proposed hearing, hold a public hearing for the purpose of obtaining information with a view to establishing, or amending or modifying, as the case may be, such official grades. The grades so established and promulgated shall include grades identical in name and requirements with all grades or standards of apples as promulgated, from time to time, by the secretary of agriculture of the United States and commonly known as the United States grades.